1. Field of Application
The present invention relates to an apparatus for controlling the timings of intervals in which combustion chamber pressure data are acquired based on output signals from cylinder pressure sensors that detect pressure within respective combustion chambers of a multi-cylinder internal combustion engine, and for controlling operating parameters of the engine based on the acquired data.
2. Description of Related Art
A related type of control apparatus is described for example in Japanese patent No. 2893233, designated in the following as reference document 1, whereby the combustion conditions within respective cylinders of a 4-cylinder internal combustion engine are judged based on output signals from four cylinder pressure sensors, with each sensor detecting the combustion chamber pressure within a corresponding one of the cylinders. With such a system in which respective cylinder pressure sensors are provided for each of the cylinders, the greater the number of cylinders, the greater will be the amounts of data obtained from the sensor signals. Thus, if data expressing the pressure detection results are obtained and processed continuously for each of the cylinders, the processing load on an electronic apparatus such as a microcomputer which operates on the data will increase in accordance with an increase in the number of cylinders.
To overcome this, it is possible to apply multiplexing to the output signals from the cylinder pressure sensors. However in that case, the greater the number of cylinders, the shorter will be the amount of time for which data can be acquired from the cylinder pressure sensor signal of any one cylinder (i.e., within each four-stroke cycle of that cylinder).
Furthermore in recent years, use of exhaust gas purification devices such as a DPF (diesel particulate filter) have come into widespread use in the exhaust systems of diesel engines. Such an exhaust gas purification device can be regenerated when necessary, by temporarily modifying the combustion conditions of the engine. This is basically achieved by delaying the timing of combustion in each cylinder by a specific amount, i.e., with respect to the compression-stroke TDC (top dead center) timing for the cylinder.
More specifically, when the engine operation is controlled to effect such regeneration of an exhaust gas cleansing device, fuel injection is performed such that combustion continues in each cylinder for a substantially long duration following the compression-stroke TDC timing. To ensure this, a small amount of fuel is injected into the cylinder in a pilot injection, prior to a main injection of fuel at a TDC timing, and similar small amounts are injected (as post-injections) after the main injection. Thus it is necessary to monitor the combustion condition within each cylinder during a substantially long range of crank angle variation, at each combustion stroke. Hence even in the case of an engine having only a small number of cylinders, if multiplexing is applied to the cylinder pressure sensor signals so that data can only be acquired periodically from each cylinder pressure sensor during a small range of crank angle variation, it becomes difficult to adequately monitor the combustion conditions within the cylinders while engine control for regeneration of an exhaust gas purification device is in progress.